A conventional solid-state imaging device has a P-type well layer formed on a surface of an N-type silicon substrate, and embedded photodiodes are formed on the surface of the P-type well layer. On the surface of the silicon substrate having the photodiodes formed thereon, an insulating film is formed. A multi-layer interconnection layer, a passivation as a surface protection film, and a color filter layer are laminated on the insulating film. Microlenses are formed on the color filter layer. The multi-layer interconnection layer has a structure in which a plurality of interconnections and a plurality of inter-layer insulating films are laminated.
The multi-layer interconnection layer in the solid-state imaging device is formed as follows. That is, after interconnection is formed on the insulating film, an inter-layer insulating film is formed on the insulating film including the interconnection. The inter-layer insulating film is made by forming a material serving as the inter-layer insulating film on the insulating film including the interconnection layer and planarizing its surface. As described above, the multi-layer interconnection layer is made by repeatedly forming the interconnection and forming the inter-layer insulating film.
In recent years, a solid-state imaging device without any color filter is desired in some cases. The inventors of the present application have discovered that if a color filter layer is removed from a solid-state imaging device, the amount of light reaching a photodiode with respect to the amount of light incident to the solid-state imaging device via microlenses (hereinafter referred to as “transmittance of the solid-state imaging device”) is different according to a wavelength. In other words, the inventors have discovered ripple occurring in transmittance characteristic of the solid-state imaging device.
This ripple is considered to be caused by an increase in the number of multi-layer interconnection layers and planarizing process of the surface of each inter-layer insulating film within the multi-layer interconnection layer by, e.g., CMP (Chemical Mechanical Polishing). More specifically, as the number of multi-layer interconnection layers increases, the distance of the incident light traveling from the microlenses to the photodiodes increases. In addition, it is difficult to diffuse the light reflected by the surface of the silicon substrate because a surface of the inter-layer insulating film is planarized. As a result, light having a particular wavelength is amplified by the interference, and light having the other wavelengths is attenuated by the interference. This is considered to result in ripple.